This invention relates to circuitry for removing information from, or modifying information in, the vertical interval of a television signal.
Various video processes add information to the vertical interval of a television signal. Frequently these signals are left in the final signal product with undesirable results. Some cable TV decoders, for example, leave white reference pulses on television lines 20-22 which can appear at the top of a monitor as a flashing bright line.
It is usual to place SMPTE time code on edited master video tapes. When a small producer uses inexpensive equipment to provide copies of these tapes, the time code will appear on the copies he supplies to his customers. Also, tapes processed with an image enhancing system as described by Faroudja in U.S. Pat. No. 4,459,613 may, on occasion, be played back without the post-processor also described in U.S. Pat. No. 4,459,613. In such a case, lines 10-16 will contain a pilot signal.
Professional environments frequently use underscanned monitors to show all four edges of the TV picture. Such monitors show ordinary VITS test signals at the top of the screen which can be quite distracting.
Previously, in order to alleviate the foregoing problems, it was necessary either to use an expensive processing amplifier or a special purpose apparatus such as the above mentioned Faroudja system. Apparatus of this kind was bulky, expensive and frequently consumed considerable power.
Also, consumer video tape recorders have a timing discontinuity near the bottom of the television screen which can be quite distracting on some monitors.
Furthermore, some television broadcasts of movies use a wide screen format wherein the full width of the television picture is matched to the full width of the original movie. Since the movie is of a wider aspect ratio than the television screen, the top and bottom of the television screen is then devoid of picture information and is sometimes filled with colored bands. This result may be annoying to a person who prefers black as would be the case in a movie theater.